Abstracts

Rationale: Electroencephalography (EEG) is an integral part of spell classification. Video EEG is the gold standard for spell classification but is not necessarily required in order to make a diagnosis. Outpatient Ambulatory EEG can also provide clinically important information in the evaluation of paroxysmal spells. This study seeks to clarify which cases are ideally evaluated by an outpatient Ambulatory EEG. Methods: After obtaining Institutional Review Board approval, a retrospective chart review was conducted of all Ambulatory EEGs obtained at Mayo Clinic in Arizona during the 10 month period between January and October 2007. A total of 66 charts were reviewed. All 6 ambulatory studies obtained during Positron Emission Tomography (PET) scans were excluded. All studies for seizure quantification in cases with established diagnoses of epilepsy were excluded. The 51 studies obtained for spell classification were included. Note was made of technical quality, clinical history, spell frequency, results of prior routine EEG and MRI scan, events captured, antiepileptic medications, and final diagnosis.Results: Of the 66 total ambulatory studies obtained in a ten month period, 51 were for spell classification. Events were captured in 57% (n=29). A diagnosis of epilepsy was made in 34% (n=10). 66% (n=19) patients ultimately received a non seizure diagnosis. In the 22 cases where events were not captured, 27% (n=6) remained indeterminate. The remaining 73% (n=16) received a diagnosis. The diagnoses were most often cardiac, psychogenic (n=5), epilepsy (n=5). It was noted that the diagnosis of PNES was confirmed in 2/5 patients after an admission to the epilepsy monitoring unit for Video EEG monitoring. Therapy changed after an Ambulatory EEG monitoring in 19% (n=10). 9 patients who had Video EEG monitoring went on to have Ambulatory EEGs, with only 1 (11%) receiving a diagnosis. Comment was made of limitations on interpretation due technical quality in 8 out of 51 cases. However, only 4% (n=2) of the studies were inconclusive because inability to interpret the EEG during the spell. Conclusions: Ambulatory EEG provides clinically important information a majority of the time, either changing medication management or guiding further clinical evaluation. Spells were captured in a 57% of cases (n=29) with a majority (65%, n=19) receiving a non seizure diagnosis. Even when spells were not captured (43% n=22), a majority of the patients ultimately were given diagnoses, which were most often non seizure (77%, n = 17). An ambulatory EEG is clinically useful in patients with paroxysmal events with neurological and non neurological phenomena in the differential diagnosis. Most of the diagnoses rendered after an Ambulatory EEG recording were non neurological and helped to rule out a seizure disorder.